The overall goal of this proposal is to investigate the cellular and molecular mechanisms underlying pulsatile gonadotropin-releasing hormone (GnRH) secretion. GnRH neurons provide the final common pathway for the central neural control of reproduction in all vertebrate species. Release of GnRH in a rhythmic manner is absolutely indispensable for reproductive function. Understanding this biological phenomenon is not only of basic interest, but also has broad application to both the enhancement and the reversible suppression of fertility. This problem will be studied in three Specific Aims, using electrophysiological, cellular and molecular techniques to investigate GnRH neurons identified by expression of green fluorescent protein. In Specific Aim I, isolated GnRH neurons will be compared with those in networks to determine possible sources of rhythmicity for episodic GnRH release. The hypotheses that individual GnRH neurons are intrinsically rhythmic but need to be organized into a network in order to generate pulsatile release at a frequency appropriate for pituitary control will be tested. The role of subcellular oscillations in generating rhythmic GnRH release and the currents underlying these oscillations will be determined. In Specific Aim II, the mechanisms coordinating GnRH neurons will be examined. The hypotheses that GnRH serves as an inhibitory neuromediator of its own release, that nitric oxide originating outside the GnRH neurosecretory network affects subthreshold activity and thereby helps coordinate GnRH neurons and that the median eminence is required for synchronization of this system will be tested. We will also conduct pilot studies to test if GnRH neurons produce traditional neurotransmitters to coordinate release by fast synaptic transmission. In Specific Aim III, the role of calcium currents in GnRH neuronal rhythmicity will be examined. The types of cell membrane calcium channels will first be determined. Then the hypothesis that these channels undergo changes in activity and/or voltage dependence due to post-translational modifications will be tested. The proposed experiments will greatly enhance our understanding of the cellular aspects of the operation of an important neuroendocrine oscillator.